Determination of lithography effective dose uniformity

ABSTRACT

Embodiments are directed to a method and system for determining effective dose of a lithography tool. The method includes performing a series of open frame exposures with the lithography tool on a substrate to produce a set of controlled exposure dose blocks in resist, and then baking and developing the exposed substrate. The method further includes scanning the resultant open frame images with oblique light and capturing the light scattered from the substrate surface. The method further includes creating a haze map from the background signal of the scattered light data, converting the haze map to a graphical image file, and analyzing the graphical image file to determine effective dose of the lithography tool, wherein a brightness of the graphical image file is related to effective dose of the lithography tool.

BACKGROUND

The present invention relates in general to the field of lithography.More specifically, embodiments of the present invention relate to thedetermination of the consistency and uniformity of lithography effectivedose.

Lithography is a process used to transcribe a pattern, such as anintegrated circuit pattern, or the like, onto a substrate. Lithographyincludes an exposure process in which a layer of resist (also known asphotoresist) on a substrate is exposed to radiation that could beelectrons, ions, soft x-ray (a.k.a. EUV) photons or optical photonsmodulated by a patterned mask. The photoresist is then developed toremove the exposed portion thereof (in the case of a positivephotoresist) or non-exposed portion thereof (in the case of a negativephotoresist), thereby forming a photoresist pattern. Then, a layer ofmaterial lying under the photoresist pattern is etched using thephotoresist pattern as a mask. As a result, a pattern corresponding tothe pattern of the mask is transcribed onto the substrate. The patterncan be used to create integrated circuit structures.

The dose and intensity of the exposure radiation should be controlled tobe uniform during the exposure process. To this end, feedback relevantto the exposure radiation can be evaluated to determine the consistencyand uniformity of the lithography process. In this respect, it becomesdesirable to accurately characterize the exposure energy being deliveredto the substrate. Control of the resist post-exposure bake and developconditions are also important to ensure consistent dose response. Itwould be desirable to determine the repeatability and uniformity of thelithography process. In this respect, it becomes desirable to accuratelycharacterize the effective dose delivered to the substrate, includingthe impacts of exposure dose and the post-exposure bake and developprocesses.

SUMMARY

Embodiments of the present invention are directed to a method and systemfor determining the effective dose of a lithography tool. The methodincludes performing a series of open frame exposures with thelithography tool on a substrate to produce a set of controlled exposuredose blocks in resist. The method further includes baking and developingthe exposed substrate. The method further includes scanning theresultant open frame images with oblique light and capturing the lightscattered from the substrate surface. The method further includescreating a haze map from the background signal of the scattered lightdata, converting the haze map to a graphical image file, and analyzingthe graphical image file to determine effective dose of the lithographytool. A brightness of the graphical image file is related to effectivedose of the lithography tool.

Embodiments of the present invention are further directed to a systemfor determining effective dose of a lithography tool. The systemincludes a lithography tool arranged to perform a series of open frameexposures on a substrate to produce a set of controlled exposure doseblocks in resist and process tools to bake and develop the exposedsubstrate. The system is further arranged to include an inspection toolto scan the resultant open frame images with oblique light and capturethe light scattered from the substrate surface. The system is furtherarranged to include software to create a haze map from the backgroundsignal of the scattered light data, convert the haze map to a graphicalimage file and perform off-line analysis to determine effective dose ofthe lithography tool from the graphical image file. A brightness of thegraphical image file is related to effective dose of the lithographytool.

Embodiments of the present invention are further directed to a computerprogram product for determining effective dose of a lithography tool.The computer program product includes a computer-readable storage mediumhaving program instructions embodied therewith. The program instructionsare readable by a processor system to cause the processor to perform aseries of open frame exposures with the lithography tool on a substrateto produce a set of controlled exposure dose blocks in resist, and thenbaking and developing the exposed substrate. The processor is furtherarranged to scan the resultant open frame images with oblique light andcapture the light scattered from the substrate surface. The processor isfurther arranged to create a haze map from the background signal of thescattered light data, converting the haze map to a graphical image file,and analyzing the graphical image file to determine effective dose ofthe lithography tool. A brightness of the graphical image file isrelated to effective dose of the lithography tool

Additional features and advantages are realized through techniquesdescribed herein. Other embodiments and aspects of the present inventionare described in detail herein. For a better understanding, refer to thedescription and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as embodiments of the presentinvention is particularly pointed out and distinctly claimed in theclaims at the conclusion of the specification. The foregoing and otherfeatures and advantages of the embodiments of the present invention areapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a pictorial representation of an exemplary scanner system;

FIG. 2 is a pictorial representation of a substrate for use in anexemplary scanner system;

FIG. 3A is a graph illustrating a non-uniform energy distribution ofexposure radiation of an exemplary system;

FIG. 3B is a graph illustrating a uniform energy distribution ofexposure radiation of an exemplary system;

FIG. 4 is flow diagram illustrating a method for characterizing anexemplary scanner system according to one or more embodiments of theinvention;

FIG. 5A is a portion of an exemplary graphic image file created by oneor more embodiments of the present invention;

FIG. 5B is an analysis of the exemplary graphic file created by one ormore embodiments of the present invention;

FIG. 5C is a graph illustrating an intensity profile created by ascanner on-board calibration;

FIG. 5D is a graph illustrating an intensity analysis performed bymeasuring exposed images from the scanner on a scanning electronmicroscope;

FIG. 6A is an exemplary graphic image file created by one or moreembodiments of the present invention;

FIG. 6B presents a portion of the exemplary graphic image file ingreater detail;

FIG. 7 is a block diagram of a computer system capable of performing oneor more embodiments of the present invention; and

FIG. 8 is a block diagram of a computer program product capable ofperforming one or more embodiments of the present invention.

The drawings are not necessarily to scale. The drawings, some of whichare merely pictorial and schematic representations, are not intended toportray specific parameters of the invention. The drawings are intendedto depict only typical embodiments of the invention, and thereforeshould not be considered as limiting. In the drawings, like numberingrepresents like elements.

DETAILED DESCRIPTION

Various embodiments of the present invention will now be described withreference to the related drawings. Alternate embodiments of the presentinvention may be devised without departing from the scope of theinvention. Various connections might be set forth between elements inthe following description and in the drawings. These connections, unlessspecified otherwise, may be direct or indirect, and the presentdescription is not intended to be limiting in this respect. Accordingly,a coupling of entities may refer to either a direct or an indirectconnection.

The terminology used herein is for the purpose of describing particularembodiments of the present invention only and is not intended to belimiting. As used herein, the singular forms “a”, “an”, and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. Furthermore, the use of the terms “a”, “an”, etc.,do not denote a limitation of quantity, but rather denote the presenceof at least one of the referenced items. It will be further understoodthat the terms “comprises” and/or “comprising”, or “includes” and/or“including”, when used in this specification, specify the presence ofstated features, regions, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or groups thereof.

In addition, it will be understood that when an element as a layer,region, or substrate is referred to as being “on” or “over”, or“disposed on” another element, it can be directly on the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on”, “directly over”, or“disposed proximately to” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or directly coupled to the other element, orintervening elements may be present. In contrast, when an element isreferred to as being “directly connected” or “directly coupled” toanother element, there are no intervening elements present.

For the sake of brevity, conventional techniques related tosemiconductor device and integrated circuit fabrication may not bedescribed in detail herein. Moreover, the various tasks and processsteps described herein may be incorporated into a more comprehensiveprocedure or process having additional steps or functionality notdescribed in detail herein. In particular, various steps in themanufacture of semiconductor devices and semiconductor-based integratedcircuits are well-known and so, in the interest of brevity, manyconventional steps will only be mentioned briefly herein or will beomitted entirely without providing the well-known process details.

Turning now to an overview of technologies that are more relevant toaspects of the invention, a general description of the semiconductordevice fabrication processes that may be utilized in implementing one ormore embodiments of the present invention will now be provided. Althoughspecific fabrication operations used in implementing one or moreembodiments of the present invention may be individually known, thedisclosed combination of operations and/or resulting structures areunique. Thus, the unique combination of the operations described inconnection with the fabrication of semiconductor devices utilize avariety of individually known physical and chemical processes performedon a semiconductor (e.g., silicon) substrate, some of which aredescribed in the following immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an integrated circuit fall into four general categories,namely, film deposition, removal/etching, semiconductor doping andpatterning/lithography. Deposition is any process that grows, coats, orotherwise transfers a material onto the wafer. Available technologiesinclude physical vapor deposition (PVD), chemical vapor deposition(CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE)and more recently, atomic layer deposition (ALD) among others.Removal/etching is any process that removes material from the wafer.Examples include etch processes (either wet or dry), andchemical-mechanical planarization (CMP), and the like. Semiconductordoping is the modification of electrical properties by doping, forexample, transistor sources and drains, generally by diffusion and/or byion implantation. These doping processes are followed by furnaceannealing or by rapid thermal annealing (RTA). Annealing serves toactivate the implanted dopants. Films of both conductors (e.g.,poly-silicon, aluminum, copper, etc.) and insulators (e.g., variousforms of silicon dioxide, silicon nitride, etc.) are used to connect andisolate transistors and their components. Selective doping of variousregions of the semiconductor substrate allows the conductivity of thesubstrate to be changed with the application of voltage. By creatingstructures of these various components, millions or even billions oftransistors can be built and wired together to form the complexcircuitry of a modern microelectronic device.

An important aspect to the above-described fabrication processes issemiconductor lithography, i.e., the formation of three-dimensionalrelief images or patterns on the semiconductor substrate for subsequenttransfer of the pattern to the substrate. In semiconductor lithography,the patterns are placed on a radiation sensitive polymer called aphotoresist. To build the complex structures that make up a transistorand the many wires that connect the millions of transistors of acircuit, lithography and etch pattern transfer steps are repeatedmultiple times. Each pattern being printed on the wafer is aligned tothe previously formed patterns and slowly the conductors, insulators andselectively doped regions are built up to form the final semiconductordevice.

Various types of exposure apparatuses can be used in lithography. Forexample, a scanner-type of exposure apparatus of a lithography systememploys an exposure slit which defines the radiation contributing to theexposure process, and a setup in which the mask and a stage supportingthe substrate are moved relative to each other so that the resist isscanned by the exposure radiation. In general, both the dose andintensity of the exposure radiation in the slit should be uniform if theexposure process is to be carried out effectively. Other exposureapparatuses also can be used. Likewise, it is important that thepost-exposure bake and develop processes are consistent and uniformsince these processes also influence the effective substrate dose.

A sensor integrated with the scanner-type of exposure apparatus may beused to measure the energy distribution of the exposure radiation. Forextensive characterization, such a sensor may take tens of minutes tomeasure the energy distribution of radiation. The exposure system is notoperated during this time. That is, there is down time in the exposureprocess, performed by a scanner-type of exposure apparatus, in which theexposure radiation is controlled based on measurements obtained using asensor.

Examples of an alternative technique for quantifying the energydistribution of exposure radiation in a scanner-type of exposureapparatus (referred to simply as a “scanner” hereinafter), and alithography method making use of such a technique, will now be describedin detail with reference to the attached drawings.

Referring first to FIG. 1, an exemplary scanner 10 includes a condenserlens 12 for condensing radiation emitted from a radiation source (notillustrated), a mask 16 having pattern corresponding to a circuitpattern to be formed on a semiconductor substrate, a slit 14 definingthe radiation condensed by the condenser lens 12 to a limited (desired)region of the mask 16, a projection lens system 18 for reducing theimage of the radiation transmitted through the mask 16 and projectingthe reduced image onto a substrate, and a wafer stage 20 provided underthe projection lens system 18 for supporting the substrate. Scanner 10may also be referred to as a stepper or a scanning stepper.

A method of exposing a substrate 20, using the scanner 10, will now bedescribed with reference to both FIGS. 1 and 2. FIG. 2 is a pictorialrepresentation of a substrate that is placed in an exemplary scannersystem. Substrate 50 in FIG. 2 may be equivalent to substrate 20 ofFIG. 1. The substrate 50 is divided into a plurality of regions 52referred to as “fields” and the fields 52 of the substrate 50 aresequentially exposed by the exposure radiation. In each field 52, anarea A (exposure slit) is projected on to the scanning substrate 50, thesubstrate 50 is moved relative to the exposure system 10 so that theexposure slit A is moved along the direction designated by the arrows inFIG. 2.

More specifically, in some embodiments of the present invention, thelength of the exposure slit A has the same dimension as each field 52 ina given direction (the direction of the X-axis in FIG. 2). As theexposure slit A in a field is exposed, the substrate 50 is movedrelative to the exposure system 10 in the width-wise direction of theexposure slit A, i.e., along the direction of the Y-axis continuouslythrough the length of field 52 and the exposure process is thenperformed again with respect to the next exposure field 52. After eachfield 52 is exposed, the substrate 50 may be moved in the direction ofthe X-axis relative to the exposure system 10 to locate the exposureslit in the adjacent field 52, and then the adjacent field region isexposed as described above by moving the exposure slit A along thedirection of the Y-axis. Thus, the substrate 50 is moved in onedirection along the Y-axis while a first field 52 is exposed, and thesubstrate 50 may be moved in the other direction along the Y-axis (i.e.,in the opposite direction) while the next field 52 is exposed.

In this manner, a resist layer formed over an entire region of thesubstrate 50 constituted by the fields 52 is exposed. Then, as mentionedabove, the resist layer is developed to thereby form a resist pattern.

Referring back to FIG. 1 and FIG. 2, the exposure radiation defined bythe slit 14 of the exposure system 10 exposes the layer of resist overeach exposure field 52. The energy distribution of the exposureradiation along the slit 14, that is, at each location along the lengthof the slit 14, should be uniform if the resist pattern to be formed bythe exposure process is to have uniform characteristics.

FIG. 3A show a non-uniform energy distribution of exposure radiationalong the slit 14. In FIG. 3A, x-axis 310 represents the distance fromthe starting point, y-axis 320 represents the radiation intensity, andgraph 330 is the graphical representation of radiation intensity at aparticular point. On the other hand, FIG. 3B shows a uniform energydistribution along the slit 14. In FIG. 3B, x-axis 360 represents thedistance from the starting point, y-axis 370 represents the radiationintensity, and graph 380 is the graphical representation of radiationintensity at a particular point. In the case in which the scanner 10 isproducing exposure radiation having a non-uniform energy distribution asillustrated in FIG. 3A, the scanner 10 is adjusted or controlled suchthat the exposure radiation has a more uniform energy distributioncloser to that illustrated in FIG. 3B. To this end, the distribution ofthe intensity of the exposure radiation passing through the slit 14 ismeasured along the length of the slit 14.

According to an aspect of the inventive concept, relationships betweenthe intensity of the exposure radiation, the oblique light scatteredfrom the residual resist in the open frame exposure blocks after thedeveloping process, and color characteristics of the haze map graphicalimage pixels, are determined and then are subsequently used to determineor “measure” the distribution of the intensity of the exposure radiationdefining the slit 14. These relationships as conceived by the presentinventors will first be described in more detail.

When a layer of a positive photoresist (referred to simply as a“photoresist layer” hereinafter) is exposed using a scanner-type ofexposure apparatus, the exposed portion of the photoresist layerundergoes a reaction which makes the exposed portion more soluble in adeveloping solution. In some cases, the exposure is followed by a bakeprocess to accelerate the exposure reaction. Thus, the exposed portionof the photoresist layer may be selectively removed by performing adeveloping process in which the exposed photoresist layer is wetted bythe developing solution. In this respect, the degree of dissolutiondepends on the dosage (level of energy) of the exposure radiation.Furthermore, when a layer of photoresist is developed, the thickness ofa layer of exposed photoresist decreases. If the delivered radiationdose is less than that required for full dissolution, the residualthickness, roughness and other surface properties depend on the dosageof the exposure radiation.

More specifically, resist dissolution does not occur when the intensityof the exposure radiation has a relatively low value. In this case, thethickness of the photoresist layer is hardly affected by the developingprocess. On the other hand, dissolution occurs throughout the thicknessof the layer of photoresist when the intensity of the exposure radiationhas a certain value, E0, known as the dose-to-clear. E0 dosage resultsin full dissolution and removal of the photoresist film. For radiationdoses above and beyond E0, the resist is also removed, though the hazemap detects evidence of surface energy changes that could be due tointeractions with the substrate. The net result is that residual filmproperties at exposure doses slightly off the E0 dose can provide a verysensitive metric of radiation dose variations.

A common method of testing lithography systems is the use of a scanningelectron microscope (SEM) to measure the feature size of developedcritical dimension (CD) images. An alternative characterizationpractice, employed open frame exposures (exposures without a maskpattern) performed on a wafer. The developed open frame images wereevaluated qualitatively via optical microscopy or quantitatively bysampling residual resist thicknesses. There are a variety ofshortcomings of such methodologies. CD SEM measurements can be limitedby feature sampling density and measurement throughput, and are affectedby non-dose related factors such as image defocus. In addition, opticalmicroscopic evaluation of open frame exposures is subjective and doesnot provide enough sensitivity. Film thickness metrology of open frameexposures provides more objective results, but the spatial frequency ofthe data collected is limited by the discrete nature of the sampling andthe low throughput of the measurements.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention address the above-described shortcomings ofthe prior art by providing a quick and accurate method and system ofanalyzing dose aspects of the lithography. The shortcomings of the priorart are overcome by graphically analyzing oblique light scattered duringa surface scan of a wafer with open frame images. This techniqueprovides high sensitivity, while allowing an analysis of a large area ofthe wafer. An analysis of high-spatial frequency surface inspection hazedata derived from the scattered light background “noise” signal can turnthe open frame test into a very powerful quantitative dose assessmenttechnique.

Turning now to a more detailed description of aspects of the presentinvention, a flowchart illustrating method 400 is presented in FIG. 4.Method 400 is merely exemplary and is not limited to the embodiments ofthe present invention presented herein. Method 400 can be employed inmany different embodiments or examples of the present invention notspecifically depicted or described herein. In some embodiments, theprocedures, processes, and/or activities of method 400 can be performedin the order presented. In other embodiments of the present invention,one or more of the procedures, processes, and/or activities of method400 can be combined or skipped. In one or more embodiments of thepresent invention, method 400 is performed by a processor as it isexecuting instructions and controlling an exemplary scanner.

An open frame exposure is performed on a wafer or substrate (block 402).The open frame wafer exposure is a traditional exposure done in a mannernow known or developed in the future. A layer of photoresist may beplaced on the wafer prior to the open frame wafer exposure. No maskpattern is used when making the open frame wafer exposure.

The full wafer exposure can produce a set of dose dependent gradedthickness blocks after resist post-exposure bake and develop steps(block 403). The wafer can be divided into multiple fields, row, orcolumns, as described in further detail below. The developed images arescanned in a defect inspection tool that detects oblique light scatteredfrom the substrate surface. The signal background levels or the noisedetected during the defect inspection of the processed open frame waferis sometimes referred to as a haze data. The “haze map” (block 404)collects this noise data from a surface scan of the entirety of thewafer.

The haze map is converted to a grayscale pixel array (block 406). Thiscan be performed in one of a variety of different manners. In someembodiments of the present invention, the gray scale pixel array can beoutput directly by the defect inspection tool. In some embodiments ofthe present invention, a high-resolution graphical image file of thewafer is output which contains the gray scale pixel details. In someembodiments of the present invention, multiple high-resolution images ofthe wafer are output by the defect inspection tool. In some embodimentsof the present invention, the images are grayscale images.

In the image(s), the surface characteristics of a particular field (suchas field 52) are represented in the pixel array as shades of gray. Thebrightness of the image at a point is related to the residual resistfilm properties (e.g. thickness, roughness, surface energy) at thatpoint and thus is related to the energy received at that point. In an8-bit example, the grayscale can range from 255 (representing E0, a dosesufficient for full removal by the development process) to 0(representing a dose significantly more or less than E0). It should beunderstood that other bit depths can be used. For example, 10-bitgraphics files could be used where 1024 different levels of gray can bedetermined. Other types of graphical files can be created. It shouldalso be understood that color images can be created instead of grayscaleimages. In such a manner, the haze map is quickly transformed from intoa graphical image that can then be analyzed using any one of a number ofdifferent graphic tools.

The pixel array can then be analyzed using one of a variety of differenttechniques (block 408). Because the array is now a graphic file in oneof a variety of different formats (for example, jpeg, png, gif, bmp,tiff, and the like), a variety of different manners can be used toperform an analysis of the graphic file. For example, analysis softwaresuch as MATLAB can be used to analyze the uniformity of the graphicfile. The analysis can translate the graphic file into multipletwo-dimensional graphs. Thereafter, the scanner energy consistency anduniformity within a field can be characterized. This enables betterunderstanding of the scanner performance limitations and can be used toverify scanner optimization strategies.

FIG. 6A illustrates an exemplary graphic file created from a haze map ofa lithographic wafer populated with an array of open frame exposures.The exemplary wafer 620 has 9 rows of fields. The rows are labeled 611through 619. As can be seen, in this embodiment of the presentinvention, each field has a different level of exposure. Any methodologycan be used to create a different level of exposure for each field, rowof fields or column of fields. In FIG. 6A, fields in row 611 receivedthe least effective dose, resulting in a darker haze map images. Fieldsin higher rows received greater effective dose. The resist clearing doseis achieved in row 615, resulting in very bright images. Even higherdoses result in darker haze map images due to additional surfaceinteractions, that is, how the surface scatters the incident obliquelight. Thus, the brightness of the graphical image file is related tothe effective dose of the lithography tool.

Of particular interest in this exemplary analysis are the fields thatreceive a bit more or less than the resist clearing effective dose, suchas row 614. The intermediate gray levels exhibited in row 614(highlighted in box 644) lead to heightened analysis sensitivity. Thisis shown in more detail in FIG. 6B where one can see vertical brightstripes corresponding to in slit dose variations. It should beunderstood that the analyses can be performed on various fields with thesame, or a range of effective doses to characterize wafer to wafer,field to field or within field effective dose variations. In addition,the identification of the clearing dose, E0, within the exposure arrayis itself a powerful tool for quantifying the wafer to wafer scannerdose repeatability.

FIG. 6B is an expanded view of five adjacent fields of row 614. Thefields are labeled 621 through 625. A close analysis of each field canreveal that, instead of the field being a uniform level of gray, therecan be areas of the field that are darker or lighter than adjacentareas. As described earlier, darker or lighter areas are indicative ofareas that received a lesser or greater amount of exposure energy. Eachof the fields can be examined in further detail by zooming in to revealgreater detail. This is shown in FIG. 5A, which is an expanded view offield 624.

In theory, FIG. 5A should be uniform. However, it can be seen that FIG.5A is not uniform. Instead, there are a variety of shades of graypresent in FIG. 5A. By analyzing the graphic image file, the shades ofgray can be converted to the amount of scanner dose delivered at thatparticular point.

FIG. 5A illustrates an exemplary graphic file 510 that was created usingfield 624. With respect to FIG. 5B, graph 520 is a left to right scanfor the average of all vertical locations in graphic file 510. One couldalso plot this across slit profile at a particular vertical location ofgraphic file 510. The X-axis 522 of graph 520 illustrates the distancealong the exposure slit from a chosen zero point. The chosen zero pointin graph 520 is at the left end of graphic file 510. The Y-axis 524illustrates the gray level at that particular point. As explained above,in an 8-bit graphic file, there can be 256 shades of gray that representdifferent effective doses. The gray level in the file for a particularslit location is related to the amount of energy received at thatlocation. It can be seen that graph 520 tracks the haze map 510, withlighter areas of haze map 510 relating to lower points of graph 520. Alower point of graph 520 indicates that a lower amount of energy reachedthe photoresist at that point.

With respect to FIG. 5C, a scanner calibration result 530 of the scannerat issue is illustrated. Calibration 530 was created using scanneron-board metrology. Some scanners used for lithography have on-boardtools that can analyze and create an energy profile. The X-axis 532represents the distance along the exposure slit from the chosen zeropoint and the Y-axis 534 represents the intensity. Graph 530 thusrepresents the radiation intensity across the exposure slit. By matchinggraph 530 with graph 520, it can be seen that graph 520 created from thegraphic image file using one or more embodiments of the presentinvention corresponds well with the scanner's own calibrated intensityprofile. In particular, localized low-points of graph 520 mostlycorrespond to low-points of graph 530 and localized high-points of graph520 mostly correspond to high-points of graph 530. However, on-boardmetrology takes a period of dedicated scanner time to sample a reducedarray of exposure slit locations sequentially unlike the normal exposuresequence where the full slit is imaged concurrently. Extensivemeasurements could take the scanner out of production for a significantportion of an hour. In contrast, embodiments of the present inventionusing open-frame exposures characterize the exposure uniformity undernormal exposure conditions. After just minutes for test wafer exposures,the scanner can resume production while an analysis using one or moreembodiments of the present invention is performed.

With respect to FIG. 5D, a scanning electron microscope (SEM) was usedto measure the width of lines between developed trenches in resist on asilicon wafer that were exposed on a lithography scanner. Graph 540includes an X-axis 542 representing distance along the exposure slitfrom a chosen zero point. Y-axis 544 is the measurement of the linecritical dimension (CD) based on the SEM analysis. Graph 540 thusrepresents the critical dimension measurement across the exposure slit.It can be seen that the critical dimension measurements of the wafer ingraph 540 correspond well with graph 530 of FIG. 5C and graph 520 ofFIG. 5B. As expected, locations receiving a higher effective dose havereduced line width and locations receiving a lower effective dose haveincreased line widths.

However, the CD SEM profile created in FIG. 5D is much more timeconsuming to generate than the on-board metrology process of FIG. 5C andthe graphic image file of FIG. 5B, created using embodiments of thepresent invention. Thus, there is a lesser tendency to generate slitprofiles on a CD SEM. In contrast, the file created in FIG. 5B can becreated very quickly (on the order of five minutes for a full wafer thatincludes 100 fields) in contrast to the hours-long process of completingthe necessary measurements on a CD SEM.

In addition, embodiments of the present invention can have much finersampling than SEM methods. CD SEM sampling is limited by the placementof appropriate measurement features. In many current CD SEM methods, 65samples per exposure field represents a “dense” sampling. In contrast,embodiments of the present invention are only limited by the resolutionof the device used to capture the haze map and generate the graphicimage file. In some embodiments of the present invention, 20,000-80,000pixels can be present in a particular exposure field, a resolution thatis 300-1200 times finer than CD SEM methods. A further advantage, isthat embodiments of the present invention are not affected by non-doserelated effects such as image defocus.

FIG. 7 depicts a high-level block diagram of a computer system 700,which can be used to implement all or part of one or more embodiments ofthe present invention. More specifically, computer system 700 can beused to implement hardware components of systems capable of performingmethods described herein. For example, computer system 700 can be usedto control a scanner or other lithography tool. Computer system 700 canbe used to perform analysis of a graphical image file created using oneor more embodiments of the present invention. Although one exemplarycomputer system 700 is shown, computer system 700 includes acommunication path 726, which connects computer system 700 to additionalsystems (not depicted) and can include one or more wide area networks(WANs) and/or local area networks (LANs) such as the Internet,intranet(s), and/or wireless communication network(s). Computer system700 and additional system are in communication via communication path726, e.g., to communicate data between them. Computer system 700 canhave one of a variety of different form factors, such as a desktopcomputer, a laptop computer, a tablet, an e-reader, a smartphone, apersonal digital assistant (PDA), and the like.

Computer system 700 includes one or more processors, such as processor702. Processor 702 is connected to a communication infrastructure 704(e.g., a communications bus, cross-over bar, or network). Computersystem 700 can include a display interface 706 that forwards graphics,textual content, and other data from communication infrastructure 704(or from a frame buffer not shown) for display on a display unit 708.Computer system 700 also includes a main memory 710, preferably randomaccess memory (RAM), and can include a secondary memory 712. Secondarymemory 712 can include, for example, a hard disk drive 714 and/or aremovable storage drive 716, representing, for example, a floppy diskdrive, a magnetic tape drive, or an optical disc drive. Hard disk drive714 can be in the form of a solid state drive (SSD), a traditionalmagnetic disk drive, or a hybrid of the two. There also can be more thanone hard disk drive 714 contained within secondary memory 712. Removablestorage drive 716 reads from and/or writes to a removable storage unit718 in a manner well known to those having ordinary skill in the art.Removable storage unit 718 represents, for example, a floppy disk, acompact disc, a magnetic tape, or an optical disc, etc. which is read byand written to by removable storage drive 716. As will be appreciated,removable storage unit 718 includes a computer-readable medium havingstored therein computer software and/or data.

In alternative embodiments of the present invention, secondary memory712 can include other similar means for allowing computer programs orother instructions to be loaded into the computer system. Such means caninclude, for example, a removable storage unit 720 and an interface 722.Examples of such means can include a program package and packageinterface (such as that found in video game devices), a removable memorychip (such as an EPROM, secure digital card (SD card), compact flashcard (CF card), universal serial bus (USB) memory, or PROM) andassociated socket, and other removable storage units 720 and interfaces722 which allow software and data to be transferred from the removablestorage unit 720 to computer system 700.

Computer system 700 can also include a communications interface 724.Communications interface 724 allows software and data to be transferredbetween the computer system and external devices. Examples ofcommunications interface 724 can include a modem, a network interface(such as an Ethernet card), a communications port, or a PC card slot andcard, a universal serial bus port (USB), and the like. Software and datatransferred via communications interface 724 are in the form of signalsthat can be, for example, electronic, electromagnetic, optical, or othersignals capable of being received by communications interface 724. Thesesignals are provided to communications interface 724 via communicationpath (i.e., channel) 726. Communication path 726 carries signals and canbe implemented using wire or cable, fiber optics, a phone line, acellular phone link, an RF link, and/or other communications channels.

In the present description, the terms “computer program medium,”“computer usable medium,” and “computer-readable medium” are used torefer to media such as main memory 710 and secondary memory 712,removable storage drive 716, and a hard disk installed in hard diskdrive 714. Computer programs (also called computer control logic) arestored in main memory 710 and/or secondary memory 712. Computer programsalso can be received via communications interface 724. Such computerprograms, when run, enable the computer system to perform the featuresdiscussed herein. In particular, the computer programs, when run, enableprocessor 702 to perform the features of the computer system.Accordingly, such computer programs represent controllers of thecomputer system. Thus it can be seen from the forgoing detaileddescription that one or more embodiments of the present inventionprovide technical benefits and advantages.

Referring now to FIG. 8, a computer program product 800 in accordancewith one or more embodiments of the present invention that include acomputer-readable storage medium 802 and program instructions 804 isgenerally shown.

Embodiments of the present invention can be a system, a method, and/or acomputer program product. The computer program product can include acomputer-readable storage medium (or media) having computer-readableprogram instructions thereon for causing a processor to carry outaspects of embodiments of the present invention.

The computer-readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer-readable storage medium can be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer-readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer-readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer-readable program instructions described herein can bedownloaded to respective computing/processing devices from acomputer-readable storage medium or to an external computer or externalstorage device via a network, for example, the Internet, a local areanetwork, a wide area network and/or a wireless network. The network caninclude copper transmission cables, optical transmission fibers,wireless transmission, routers, firewalls, switches, gateway computers,and/or edge servers. A network adapter card or network interface in eachcomputing/processing device receives computer-readable programinstructions from the network and forwards the computer-readable programinstructions for storage in a computer-readable storage medium withinthe respective computing/processing device.

Computer-readable program instructions for carrying out embodiments ofthe present invention can include assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including anobject-oriented programming language such as Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. Thecomputer-readable program instructions can execute entirely on theconsumer's computer, partly on the consumer's computer, as a stand-alonesoftware package, partly on the consumer's computer and partly on aremote computer or entirely on the remote computer or server. In thelatter scenario, the remote computer can be connected to the consumer'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection can be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments of the present invention,electronic circuitry including, for example, programmable logiccircuitry, field-programmable gate arrays (FPGA), or programmable logicarrays (PLA) can execute the computer-readable program instructions byutilizing state information of the computer-readable programinstructions to personalize the electronic circuitry, in order toperform embodiments of the present invention.

Aspects of various embodiments of the present invention are describedherein with reference to flowchart illustrations and/or block diagramsof methods, apparatus (systems), and computer program products accordingto various embodiments of the present invention. It will be understoodthat each block of the flowchart illustrations and/or block diagrams,and combinations of blocks in the flowchart illustrations and/or blockdiagrams, can be implemented by computer-readable program instructions.

These computer-readable program instructions can be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer-readable program instructionscan also be stored in a computer-readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that thecomputer-readable storage medium having instructions stored thereinincludes an article of manufacture including instructions whichimplement aspects of the function/act specified in the flowchart and/orblock diagram block or blocks.

The computer-readable program instructions can also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams can represent a module, segment, or portionof instructions, which includes one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block can occur out of theorder noted in the figures. For example, two blocks shown in successioncan, in fact, be executed substantially concurrently, or the blocks cansometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The terminology used herein is for the purpose of describing particularembodiments of the present invention only and is not intended to belimiting. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription has been presented for purposes of illustration anddescription, but is not intended to be exhaustive or limited to the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art without departing from the scope andspirit. The embodiments of the present invention described herein werechosen and described in order to best explain the principles ofembodiments of the invention and the practical application, and toenable others of ordinary skill in the art to understand the variousembodiments of the present invention with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A system for determining effective dose of alithography tool comprising: a lithography tool arranged to perform aseries of open frame exposures on a substrate to produce a set ofcontrolled exposure dose blocks in resist; process tools to bake anddevelop the exposed substrate; an inspection tool to scan the resultantopen frame images with oblique light and capture the light scatteredfrom the substrate surface; software to create a haze map from thebackground signal of the scattered light data and convert the haze mapto a graphical image file; and off-line analysis to determine effectivedose of the lithography tool from the graphical image file, wherein abrightness of the graphical image file is related to effective dose ofthe lithography tool.
 2. The system of claim 1 wherein performing theopen frame exposure comprises: depositing photoresist on the substrate;and performing a pattern-less exposure of the substrate.
 3. The systemof claim 2 wherein performing a pattern-less exposure comprises:dividing the substrate into a plurality of fields, rows, or columns; andproviding each field, row, or column of the substrate with a differentamount of effective dose.
 4. The system of claim 1 wherein the analysisof the graphic image file comprises: determining a brightness of theimage file for a plurality of points of the graphic image file; andusing the brightness to determine energy output of the lithographytools.
 5. The system of claim 4 wherein the system is further arrangedto: use the energy output determination to characterize the wafer towafer dose consistency of the lithography tool.
 6. The system of claim 4wherein the system is further arranged to: use the energy outputdetermination to characterize the within field dose uniformity of thelithography tool.
 7. The system of claim 1 wherein generating the hazemap graphical image file comprises: scanning the resultant open frameimages with oblique light and capturing the light scattered from thesubstrate surface using an oblique light inspection device; creating ahaze map from the background signal of the scattered light data;converting the haze map to a graphical image file.
 8. The system ofclaim 7 wherein the oblique light inspection device is a defectinspection tool.
 9. A computer program product for determining effectivedose of a lithography tool comprising: a computer-readable storagemedium having program instructions embodied therewith, the programinstructions readable by a processor system to cause the processorsystem to: perform a series of open frame exposures with the lithographytool on a substrate to produce a set of controlled exposure dose blocksin resist; bake and develop the exposed substrate; scan the resultantopen frame images with oblique light and capture the light scatteredfrom the substrate surface, using an oblique light inspection device;create a haze map from the background signal of the scattered lightdata; convert the haze map to a graphical image file; and analyze thegraphical image file to determine effective dose of the lithographytool, wherein a brightness of the graphical image file is related toeffective dose of the lithography tool.
 10. The computer program productof claim 9 wherein performing the open frame exposure comprises:depositing photoresist on the substrate; and performing a pattern-lessexposure of the substrate.
 11. The computer program product of claim 10wherein performing a pattern-less exposure comprises: dividing thesubstrate into a plurality of fields, rows or columns; and providingeach field, row or column of the substrate with a different amount ofexposure dose.
 12. The computer program product of claim 9 whereinanalyzing the graphic image file comprises: determining a brightness ofthe image file for a plurality of points of the graphic image file; andusing the brightness determination to determine energy output of thelithography tools.
 13. The computer program product of claim 12 whereinthe system is further arranged to: use the energy output determinationto characterize the wafer to wafer dose consistency of the lithographytool.